i'm supposed to film with the varicam and digiprimes and was wondering about the (white) shading. how to do it and why..i'm not too familiar with hd cams so maybe someone out there has an answer for me.

The White Shading feature provides control over the individual red, green and blue channel gains so that non-standard color balance can be achieved. (as defined by Pixelink) It is more commonly known as "white balance". In photography and image processing, color balance (sometimes gray balance, neutral balance, or white balance) refers to the adjustment of the relative amounts of red, green, and blue primary colors in an image such that neutral colors are reproduced correctly. Color balance changes the overall mixture of colors in an image and is used for generalized color correction. (from Wikipedia)

As to how to do it. Set a white card under the lighting conditions you're shooting in. Zoom into that white card so that fills, or almost fills, your frame. There's a button in the front-bottom of the camera that you press labeled AWB, or Automatic White Balance. The camera will need to be set to either White Balance selector A or B. The other way is by manually adjusting the red, green and blue channels within the camera's menus to achieve the desired color balance.

At the risk of casting aspersions, you've got some reading to do before your shoot if you're asking such fundamental questions. Most of this information is available in the manual.

First note is don't do this yourself. Let the rental house prep this for you. Good news is that this is an automatic process on the Varicam, so if the techs know the basics they won't mess it up.

Essentially, white shading is setting every pixel to a common level of white reference based on the specifics of what your lenses are passing through. The way to set this is to point your lens at a perfectly even and white surface (we use an integration sphere, which is like the inside of a huge ping pong ball). Find an auto white balance and set the exposure to 70% ire and then perform the white shading. This will set an offset for each and every photosite on the three sensor chips to create a perfect white reference. This can be saved as a lens file on the camera and all your glass should now match.